The carbostyril derivatives of the formula (1) and their salts are known and disclosed, for example, in EP-A-0355583 and U.S. Pat. No. 5,053,514, wherein it is disclosed that these compounds have myocardial contract increasing activity (i.e. positive inotropic activity), coronary blood flow increasing activity, hypotensive activity, an activity of inhibiting blood vessel contract induced by norepinephrine, and antiinflammatory activity and are useful as cardiotonics for the treatment of heart diseases, hypotensives and antiinflammtory. It has also been disclosed in EP-A-0531548 that these compounds have platelet aggregation inhibitory activity, phosphodiesterase inhibitory activity and cerebral blood flow increasing activity and are useful as an agent for treating thrombosis and as a phosphodiesterase inhibitor.